THE INTEROSSEOUS MUSCLES. 211 



metatarsal bones at their anterior extremity. A thin fascia covering 

 the interosseous muscles is attached to its hinder edge. It is con- 

 cealed by the adductor transversus hallucis, and by the tendons, 

 vessels, and nerves of the toes. 



Dissection. To complete the dissection of the last layer of Dissect the 

 muscles, the flexor brevis minimi digiti may be detached and 

 thrown forwards. Dividing then the metatarsal ligament between 

 the bones, the knife is to be carried directly backwards for a short 

 distance in the centre of each interosseous space, except the first, 

 in order that the two interosseous muscles may be separated 

 from each other. All the interossei are visible in the sole of 

 the foot. 



The fascia covering the muscles should be taken away if any 

 remains, and the branches of the external plantar nerve to them 

 should be dissected out. 



FOURTH LAYER OF MUSCLES (fig. 79). In the fourth and last Fourth 

 layer of the foot are contained the interosseous muscles, and the muscles, 

 tendons of the tibialis posticus and peroneus loiigus. 



The IXTEROSSEOUS MUSCLES (fig. 79) are situate in the intervals interossei. 

 bt-tween the metatarsal bones : they consist of two sets, plantar and 

 dorsal, like the interossei in the hand. Seven in number, there are 

 three plantar and four dorsal ; and two are found in each space, 

 except the innermost. 



The plantar //*//.-W<x (o) aiv slender fleshy slips, belonging to the Three plan- 

 ,,5 ^ i t j j c tar for three 



outer three toes. Each arises from the under and inner surrace 01 outer toes, 

 the corresponding metatarsal bone (fig. 76, p. 201) ; and is inserted 

 partly into the tibial side of the base of the first phalanx of the 

 same toe, and partly by an expansion to the extensor tendons oil 

 the dorsum of the phalanx. These muscles are smaller than the 

 dorsal, and are placed more in the sole of the foot. 



The dorsal muscles (i), one in each space, arise by two heads Four dorsal 

 from the lateral surfaces of the bones between which they lie, bones, 

 (fig. 76), and are ii)s>:rti.'d like the others into the side, and on the 

 dorsum of the metatarsal phalanx of certain toes. Thus, the inner 

 two muscles belong to the second toe, one to each side ; the next 

 belongs to the outer side of the third toe ; and the remaining one 

 to the outer side of the fourth toe. 



The interossei are crossed by the external plantar vessels and Relations, 

 nerve, and their digital branches ; and they lie beneath the 

 adductor transversus hallucis and the metatarsal ligament. The 

 posterior perforating arteries pierce the hinder extremities of the 

 dorsal set. 



Action. Like the interossei of the hand (p. 81), they will^'seas 

 contribute to the bending of the metatarso-phalangeal joints, and * 

 straighten the two interphalangeal joints. extensors; 



They can act also as abductors and adductors of the toes. Thus, as adduc- 

 the plantar set will bring the three outer toes towards the second tors> 

 toe ; and the dorsal muscles will abduct from the middle line of the 

 second toe, the two attached to that digit moving it to the right 

 and left of the said line. 



P 2 



